1. Field of the Invention
The present invention relates to a small-scale triaxial antenna coil, that is used in a receiver or the like of a radio-controlled keyless entry system and a crime-prevention device.
2. Description of the Related Art
An antenna coil is used in a receiver or the like of a keyless entry system and a crime-prevention device, that are widely used in vehicles and the like. Recently, instead of a conventional antenna coil that includes a plurality of rod-like ferrite cores with windings around them for receiving waves in their respective directions, there is being used a miniaturized triaxial antenna coil that is installed in one part of a miniaturized receiving apparatus and can receive waves in all directions, as shown in FIGS. 4 and 5.
FIG. 4 is a perspective view of a conventional antenna coil, and FIG. 5 is a perspective view of the coil section of FIG. 4 (Cf. Japanese Laid-Open Patent Application No. 2003-92509). This antenna coil includes a core 15, comprised of ferrite and formed in a flattened drum-like shape, a first coil 25, wound around the Y-axis of the core 15, a second coil 26, wound around the X-axis of the core 15, and a third coil 27, wound around the Z-axis of the core 15. Wind grooves 21, 22, and 23, are provided in the sections where the first, second, and third coils are wound.
As shown in FIG. 4, the coil 20 that is wound in this manner is stored in a resin case 28 having four external terminals 29 on two opposing faces. Three winding terminals of the coil 20 are electrically connected to specified external terminals.
In conventional antenna coils such as that described above, when winding the first, second, and third coils, the terminal of the winding that was wound first must be momentarily held in another position while the next winding is wound. This operation is complex, and the winding terminals sometimes snap. In the assembly process of storing the coil 20 in the case 28, each winding terminal must be connected to an external terminal, leading to problems such as snapping and the like during binding, and increasing the number of necessary operations. Connecting electrodes directly to the faces of a core that does not use a case results in problems of high deterioration in Q caused by the electrode faces, the electrodes peel off easily, and core loss on the electrode faces.